Identifying the Factors Necessary for Successful DNA Profiling from Spent Cartridge Casings

As submitted by the proposer: Firearms were used in about a third of the 1.2 million violent crimes in the U.S. in 2011, including in more than two thirds of all U.S. homicides. Given this, identifying an individual who utilizes a firearm is extremely important. However, often the only firearm-specific items remaining from a shooting are spent cartridge casings, which for many weapons are automatically ejected. Since cartridges were presumably loaded by the shooter, spent casings have the potential to be highly probative. Unfortunately, any fingerprints that may have been deposited during loading are virtually always destroyed by the high temperatures reached in the firing chamber. Owing to this, some crime laboratories have attempted to analyze DNA from spent casings, with the thought that the loader may have left a few cells on them. Generally the casings are swabbed and analyzed under the laboratory's SOP for other evidence types, with no compensation for the highly compromised genetic material likely to be present on them. These efforts rarely, if ever, lead to development of STR profiles. If DNA analysis from spent cartridge casings is to become a viable forensic tool, research needs to be undertaken on how to optimize its collection and analysis, which are the goal of the proposed studies. Based on published research, the research conducted in our laboratory, and personal communications with the Michigan State Police (MSP) Forensic Science Division, a series of studies has been designed to address the following questions: How does processing a casing for fingerprints (cyanoacrylate fuming) compare to not processing it, with regard to DNA yield and profiling success? How does swabbing a casing using different wetting solutions compare to soaking it, with regard to DNA yield and profiling success? How does an organic extraction compare to a commercial silica-based kit extraction, with regard to DNA yield and profiling success? How do swabbing strategies (swabbing casings individually versus swabbing multiple cartridges with a single swab) influence DNA yield and profiling success? How do different STR kits influence the success of DNA profiling from casings? How does the caliber of the ammunition influence DNA analysis? How does the success and probative value of nuclear DNA testing of casings compare to that of mtDNA analysis, given the strengths and weaknesses of each? Volunteers, under the supervision of MSP Forensic Science Division will load pistol magazines with cartridges at an MSP forensic laboratory, and also provide a buccal swab. Swabs and cartridges will be record linked to each other but completely de-identified from the volunteers (the work has already received Michigan State University IRB approval). Weapons will be fired by MSP personnel and casings will be collected, bagged, and assigned to the individual experimental protocols. A series of side by side comparisons will be made, noting how each influences DNA yields (Quantifiler) and DNA typing (STR kits, mtDNA) from spent casings. These include fumed and non-fumed casings, different swab wetting solutions, single or double swabbing, soaking casings, and singly or cumulatively swabbing casings. The resultant DNAs will be tested using Identifiler, Powerplex, and Minifiler, and the number of alleles generated, along with alleles not consistent with the loader, will be assessed. mtDNA testing will also be conducted in order to compare successful analysis rates to those of STRs. Different cartridge calibers will be examined to see how they influence DNA yields and profiles. Along with required financial reports, semi-annual and final Progress Reports will be produced as well as a Final Research Report, Abstract, and Executive Summary. In the end, this broad range of studies is designed to identify strategies for testing spent cartridge casings that result in much higher rates of DNA based identifications than are being generated today.

ca/ncf